Means for measuring the altitude of aircraft



J y 1939- M. BAESECKE Q Z MEANS FOR MEASURING THE ALTITUDE 0F AIRCRAFTFiled April e, 1938 -50NIC ALTIMETER SONIC ALTIMETER "'68 7s V :1 qg v.77 f 3 Ta INVENTOR.

ATTORNEY.

Patented July 25 1939 ras . ZJWAIZ MEANS FOR MEASURING THE ALTITUDE OFAIRCRAFT Martin Baesecke, Berlin- Siemensstadt, Germany,

Application April 6, 1938, Serial No. 200,526

Germany November 13,1934

8 Claims. (Cl. 73-4) This invention relates to a means for measuring thealtitude of aircraft and in particular to a'means for Obtaining acorrected altitude indication for distribution to a plurality oflocations in a single aircraft or for distribution to a plurality ofaircraft flying in'a group.

It is highly desirable that an accurate indication of the altitude ofanaircraft be obtained, for example, when the craft is controlled byaltitude responsive means. It is also desirable and necessary in groupflying, that the altitude of each craft concerned be gauged by that ofthe other members of the group.

One of the objects of the present invention is to provide novelmeans forobtaining an accurate indication of the altitudeof 'an aircraft aboveground rather than above a common da- A further object is to provide anovel means for indicating the altitude of an aircraft at a plurality oflocations within the craft.

Another object is to provide a novel method for controlling thealtimeters of a number of aircraft flying as a group wherein a nasteraltimeter upon one of the craft constitutes 9. reference for thealtimeters upon the other members of the group.

An additional object is to provide, for use in aircraft, an altimeterwhich continuously indicates the altitude relative to any predetermineddatum, such as sea level, and which is automatically and periodicallycorrected by an altimeter which gauges the altitude relative to "theearth directly beneath the aircraft,

1 The above and further objects and novel features of the invention willmore fully appear from the followingdetailed description, when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, hOWBVGI thBt the drawing is forthe purpose ofillustration only. and is not intended to define. the limits of theinvention, reference being had for this latter purpose to the appendedclaims.

In the drawing, wherein like reference characters refer to like partsthroughout the several views,

Fig. 1 is a schematic-diagram of one embodi- -mentof;a master altitudegaug n v Fig. 2 is a schematic diagram of a second em- 1 bodiment of themaster altitude gauge.

The form of the invention illustrated in the accompanying drawing by wayofexample is a device for providing at a plurality of locations on anaircraft a continuous indication of the flying altitude relative to theearth directly therebeneath, rather than relative to a single datum, I

. as sea level. At one of these locations, a master apparatus isprovided comprising an altimeter which operates continuously, forexample, one of the barometric type which measures the altitude relativeto sea level and which is associated witha second altimeter, forexample, one of the sonic type which is operated periodically only andmeasures the altitude relative to the earth beneath the craft. Through acomparison of the readings of the two gauges, the first one isautomatically corrected. At each additional '10- cation upon the samecraft, a repeating indicator, which is operatively connected to thebarometric altimeter, may be employed. If it is-desired to. providealtitude indications at' a plu-' rality of locations each upon adiiferent aircraft constituting a member of' a-group, then a masterapparatus as above described may be employed upon one of the aircraft.Upon the other craft, a continuously operating single altimeter may beused, for example, a barometric altime'ter which, by radio communicationat predetermined intervals, may be compared to the master apparatus andcorrected. While the sonic gauge is operated only from time to time tocorrect the barometric gauges associated therewith, the latter willprovide a suiiiciently accurate running indication of the altitude.

In the form illustrated in Fig. 1, the novel altitude measuringapparatus comprises a sonic altimeter l0, known per se, which bymeasuring the sounding'intervaL-i. e., the length of time required by asound impulse, generated at the plane, to strike the earth and return,determines the altitude of the craft. A continuously operatingbarometric gauge is employed in conjuncgauge may be automaticallycorrected by the altitudes obtained periodically at gauge ID, athermionic tube circuit is employed wherein a discrepancybetween thegauge indications changes the grid current of said circuit and actuatesa mechanism to correct the barometric gauge. A

conventional thermionic tube i7 is provided hav ing a plate l8, a grid19, and a filament 20. A condenser 2! is connected in the grid circuit,in

of the barometric altitude.'

a known manner, in parallel with a resistance 22 across leads 23, 24.Condenser 2| is operatively connected -to' the shaft of gear l3 suchthat the capacity thereof is a function of the movement of thebarometric-vessel 'l I. The condenser is charged by a. constantpotential battery 25, through a resistance 26, when the grid circuit isclosed by a switch 21 which is normally held in an open position by a.spring 21a, and is controlled by a solenoid 28 .having a plunger 29..Suitable means (not shown) associated with gauge l cause solenoid 28 tobe energized, and the grid circuit thus to be closed, during.thesounding interval of gauge Ill.

The means for adjusting the barometric gauge when the grid potentialchanges comprises a pair of relays 30, H in series upon a lead 32 in theanode circuit. Each of said relays is operable at a different currentand is in series with the constant potential battery 33 which undernormal,

conditions'provides a-current which isbetween those values necessary tooperate said relays. The relays control the direction of operation of amotor 34, having a shaft 34a, by means of a double arm switch 35 havingarms 35a and 35b which are respectively associated with relays 30, 3|.Arms 35a, 35b are connected to motor 34 by a lead 35 through an energysource 31 and may engage a lead 38 or 39, respectively, in accordancewith which relay is actuated, to produce right or left rotation of shaft34a. Shaft 34a is operatively connected to vessel II by means of a worm40 thereon which meshes with a worm wheel portion 4| which is rigidlyattached to the above-described lever I6 and linked to vessel H by therod I5.

In order that the altitude indication vessel ll-may be distributed to aplurality of locations in a single aircraft, the torque of the shaft ofpointer I4 may be amplified by suitable means and distributed, forexample, by synchronous motors in a manner as shown for example in theU. S. Patent to Reichel et al. 2,038,059, dated April 21, 1936'. Insteadof a continuous automatic distribution, the additional indicators may beof the barometric type and may be manually adjusted to agree with thedouble apparatus. Thus, where all the gauges are at the same altitude, acorrection for one gauge is applicable to all gauges. However, in thecase of group flying, the circumstances are different because themembers of the group are frequently at different altitudes and in orderfor a correction, as determined by the master gauge upon one of thecraft, to be applicable to the barometric gauge on the other craft, allof said barometric gauges must possess the same characteristics and beadjusted alike at the beginning of the flight. As above mentioned, theindications of the various single barometric altimeters in the separateaircraft may be corrected to agree with the master by periodic radiosignals from the craft having said master apparatus. 4

In operation, when flying at a given altitude, an altitude indication isobtained from the sonic gauge ll. During the sounding interval,

the grid circuit of tube I1 is closed by solenoid 28. A charge is builtup in condenser 2| which is dependent upon, first, said soundinginterval, and second, the overlapping area. of the condenser plates',which area is, in turn, a function This condenser charge controls thegrid potential and is initially predetermined at such a value that theplate current, governed thereby, holds relays 30, II in the openposition, i. e., the current is between those values which will actuatesaid relays. If the barometric altitude is in agreement with thealtitime determined by gauge It! then the charge upon said condenserwill not alter the grid potential from the predetermined value and themotor 34 will not be energized, hence no adjustment will be communicatedto vessel ll If the altitude, for example, increases then the soundinginterval also increases and the capacity or overlapping plate area ofthe condenser should decrease correspondingly in order that the chargeupon the condenser will remain constant at the predetermined value.However, if an altitude change occurs at gauge [0, and this change isnot followed by vessel II, the discrepancy will be reflected in a changeof the charge upon the condenser. This change', in turn, will disturbthe constant plate current and will actuate either re.- lay 30 or 3| inaccordance with an increase or decrease in said current. Motor 34 willthus be energized and will adjust, by means of the lever I6 and rod l5,the vessel II "and the capacity of .condenser 2!, such that the propergrid potential is restored. When thegrid potential is restored, theplate current will regain its former value and motor .34 will come torest.

In the form shown in Fig. 2, a barometric gauge having a vessel 42 'isemployed in con-' junction with a second periodically operated sonicaltitude gauge 43, which, instead of determining the altitude from asingle sounding interval, as in the first embodiment, directs a seriesof sound impulses against the earth and obtains the altitude bydetermining the frequency of said impulses when they are transmitted andreceived simultaneously. This type of altitude gauge is known per se andconstitutes no part of the invention. The altitude responsive frequencymay control, by suitable means, the frequency of an electric currentand, in a manner to appear hereafter, also control said barometricgauge. I

Centrally attached to the vessel 42 of the gauge is a rack 44 meshingwith a gear '45 which positions a pointer 46 upon an altitude scale .41.A second gear 48 also meshes with rack 44 and controls, by an arm 49, avariable resistance 50 which lies in the circuit of a glow lamp withwhich, for example, means are associated whereby the current isperiodically turned on and 01!. Arm 49 is connected to resistance 50 bya lead 52 on which, in series, are said lamp, a primary coil 53 of atransformer 54, and a suitable source of electric energy 55. A condenser56 connected in parallel with said lamp and coil and in series with lead52, said source 55, resistance 50 and lead 52 Condenser 56 is charged bythe source 55. -As soon as the condenser 55 builds up to the propervalue, the glow lamp 5| breaks down" and the circuit is-closed. Once thecircuit is closed, condenser 55 discharges, thereby setting up a sourceof current through coil 53. As the condenser continues to discharge, itscharge reaches a value below the break down point of the glow lamp andthe circuit is broken. The condenser again charges and the cy'le isrepeated. The number of said dischar es determines the frequency. 'Asthe value of resistance 50 increases, the charging time. of condenser 55increases and hence the frequency decreases and as the value ofresistance 50 decreases; the charging time of condenser 56 decreasesandthe frequency increases. The frequency of the flashes of lamp 5! and ofthe current in the-connected 7 2,167,412 circuit is therefore controlledby resistance '50 and hence by the barometric altitude.

In order that any descrepancles between themdications of the gaugeincluding vessel 42 and the gauge 43 may be eliminated, novel means areto revolve disc til in opposite directions at equal" speeds. Disc til isoperatively connected at ves- Sci d2 by a centrally. disposed shaft 6|having a worm 62. thereon, meshing witha worm wheel sector 63 which isrigidly attached to a lever 66 pivotally mounted at Ma. Lever 6d bymeans of a rod 55 centrally attached to vessel 42;, opposite rod 88, islinked to-said vesssel.

Rollers 58, 59 normally may-rotate freely upon shaft Ella butelectro-magnetic couplings (not shown) are provided thereonwhich causethe rollers to grip said shaft. The electro-magnetic couplings may befed ov'er suitable slip rings (not shown) upon the rollers. The exciterwindings for said couplings are schematically represented by coils t8,6?.

leads t8, t9 andcoil 67 in turn is connected to gauge 53 through atransformer 10 by leads ll, l2.

In order that a plurality of altitude indicators may be controlled bythe gauge including vessel 62, a primary coil 73 of a transformer it isconnected in lead til. A secondary coil E5 of the transformer isconnected to a plurality of indicators, for example, frequency meters76, ll which are calibrated to measure altitude.

In operation, the gauge 43 is actuatedduring a snfiicient length of timeto obtain an indication of the altitude above ground. A pulsating current will be produced in coil 81 having a fre-, quency which isresponsive to this indication.

The barometric gauge by controlling the variable resistance 5t governsthe frequency of the flashing of lamp El, and hencethe frequency of thecurrent in transformers 54 and I l and in coil 66. These altituderesponsive frequencies are compared by means of the coils 68, 61 which,when energized electro-magnetically couple rollers 58, 59 to shaft 57aand cause disc 60 to rotate. If the frequency of the two currents isequal, the eldctlD-Illagfifiilic couplings in the rollers will beenergized equal lengths of time during, for example, one second, and thesummation of the impulses tending to rotate disc 60 clockwisewill equalthe summation of impulses tending to rotate the disc in the oppositedirection with a net result of zero rotation. However, if the frequencyof the current in one coil becomes greater than that in the other,responsive to a difference in. the altitude indications, the rollerassociated with the coil having the higher frequency will be coupled toshaft We the greater, length of time during any given period.Conseqaent'lfi disc will be rotated in accordance with the difieren'cein saidfrequencies and will adiustwessel 62 and resistance 56 to bringthe frequency of coil 66 into agreement with that of coil 61' and thusto bring the indication of vessel E2 into coincidence with that ofaltimeter E3.

The former coil is in connection with the secondary of transformer 56 bymeans of There is thus provided a novel altitude gauging apparatus whichprovides a continuous corrected altitude above ground. The device isadapted for use in group flying wherein the gauges of the members of thegroup may be corrected by reference to a master apparatus. The device isalso we'l adapted for controlling and adjusting a plurality of altitudeindicators upon a single craft. The novel apparatus is automatic inoperation and simple in construction and furthermore is 10 well adaptedfor use aboard aircraft.

Although only two embodiments have been i lustrated and described indetail, it is to be expressly understood that the invention is notlimited thereto, and that various changes may be 15 made in the designand arrangement of the parts illustrated without departing from' thespirit andscope of the invention as the same will now be understood bythose skilled in the art. For a definition of the limits of'theinvention, reference 2W will be had primarily to the appended claims.

What is claimed is: 1. The combination with an altimeter for measuringthe altitude of an aircraft relative to a single datum, a secondaltimeter measuringfid altitude relative to the earth beneath theaircraft, and means operable in response to a discrepancy between theindications of said altimeters for bringing the indication of thefirst-nam8d altimeter into coincidence withthe indications of thesecond-named altimeter.

2. The combination with an altimeter measuring altitude relative to asingle datum, of a second altimeter measuring altitude relative to thesurface of the earth beneath said altimeters, $5

means for adjusting the indication of the firstnamed altimeter, andmeans for actuatingsaid adjusting means in response to differences inthe indications of said altimeters.

a. The combination with a barometric altitude to gauge of a sonicaltitude gauge, means for producing an electric impulse at apredetermined of said gauges Y potential "when the indications are incoincidence, said means being adapted for changing the potential of saidimpulse in re- 45 sponse to discrepancies between the indications ofsaid gauges, and means operable in response to changes in said potentialto adjust the indication of said barometric gauge.

4. The combination with a gauge for meas- 5a uring the vertical distanceof a vehicle from a 4 single datum, of a second "gauge for measuring theverticaldistance of said vehicle from the earth, means for producing aseries of impulses having a frequency responsiveto the indication 65 ofthe first-named gauge, means for producing aseries of impulses having afrequency responsive to the-indication of the second-named gauge, meansfor comparing the frequencies of impulses to discrepancies in saidfrequencies for adjusting the indication ofsaid first-named gauge.

5. The combinatio'njwith a continuously operating altimeter-formeasuring altitude relative to a single datum of a second altimeter formeasuring altitude relative to the earth, means for producing impulsesata frequency responsive to the indications of the first-namedaltimeter. means for producing impulses at a frequency produced by saidmeans, and means responsive e0 responsive to the indications of thesecond 'go named altimeter, and means for adjusting said first-namedaltimeter in response to the dinerence between said frequencies.

6. In apparatus of the class described, a barometric altimeter, a sonicaltimeter, means for E8 producing current impulses at a frequencyresponsive to the indications of the barometric altimeter, means forproducing current impulses at a frequency responsive to the indicationsof the sonic altimeter, a servo-motor, means for operatively connectingsaid motor to the barometrio altimeter in response to the difierencbetween said frequencies whereby said barometric altimeter is broughtinto agreement with said sonic altimeter, a plurality of altitudeindicators, and means for operatively connecting said indicaters to saidbarometric altimeter.

7. The combination with an altimeter for gauging the altitude of anaircraft above a single datum, of a second altimeter for gauging thealtitude of an aircraft relative to the earth directly therebeneath, avariable condenser, means for controlling the capacity of said condenserin accordance with the indications of the first-named altimeter, meansfor controlling the charging time of said condenser in accordance withthe indications of said second altimeter whereby a constant potentialacross said condenser is maintained when "the indications of saidaltimeters 'are in coincidence, and means operable in ac-

